Solvent deasphalting with two light hydrocarbon solvents

ABSTRACT

The invention deals with a method and apparatus for treating asphaltic feed stock in which high-molecular-weight hydrocarbon solvent is introduced into a compartmentalized contacting tower below the feed stock, and a low-molecular-weight hydrocarbon solvent is introduced above the feed stock. The high-molecularweight solvent is an alkane or alkene hydrocarbon containing from three through seven carbon atoms inclusive and the low-molecularweight solvent consists of an alkane or alkene hydrocarbon containing from two through six carbon atoms, with the lowmolecular-weight solvent having at least one less carbon atom than the high-molecular-weight solvent.

United States Patent PETROLEUM RES/DUE F E E D 2,213,798 9/1940 Anne 208/309 2,601,674 6/1952 Reman. 23/2705 3,150,934 9/1964 Hazard 208/309 3,414,506 12/1968 Campagne 208/309 Primary Examiner-Herbert Levine An0rneysJohn E. Wilson, John Maier, ill and Marvin A.

Naigur ABSTRACT: The invention deals with a method and apparatus for treating asphaltic feed stock in which high-molecular-weight hydrocarbon solvent is introduced into a compartmentalized contacting tower below the feed stock, and a lowmolecular-weight hydrocarbon solvent is introduced above the feed stock. The high-molecular-weight solvent is an alkane or alkene hydrocarbon containing from three through seven carbon atoms inclusive and the low-molecular-weight solvent consists of an alkane or alkene hydrocarbon containing from two through six carbon atoms, with the low-molecular-weight solvent having at least one less carbon atom than the highmolecular-weight solvent.

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WT SOLVENT IN PE TROL E UM RES/DUE FEED HIGH MOL. WT SOLVENT IN sozvtwr AsPFALr u/x r0 nscovmr srsrew ATT 'O ZEY SOLVENT DEASPHALTING WITH TWO LIGHT HYDROCARBON SOLVENTS BACKGROUND OF THE INVENTION Petroleum residue is composed of asphaltic components and nonasphaltic components which are usually referred to respectively as asphalt and deasphalted oil. The separation of the deasphalted oil from the asphalt is generally achieved through the use of light hydrocarbon solvents which exhibit preferential solubility with respect to the deasphalted oil. The separation takes place in contacting devices which afford multiple-stage countercurrent contacting of the solvent and petroleum residue. There is a variety of equipment used for the separation, such as mixer-settlers, baffled towers, centrifugal contactors, tray towers, and mechanical agitators, and this type of separation is generally referred to in the art by the following terms: deasphalting, decarbonizing, deresining or deasphaltening. The present invention is applicable in connection with any variety of contacting devices such as those referred to above, in which deasphalting can be accomplished.

In the past, deasphalting solvents have been used consisting of alkane or alkene hydrocarbons containing from two through seven carbon atoms. The choice of a solvent for a particular deasphalting operation is usually made on the basis of the deasphalting yield. For example, propane is commonly used when a relatively low yield of low-viscosity deasphalted oil is required, whereas butane is commonly employed for higher yields of more viscous deasphalted oil, and mixtures of propane and butane are used for intermediate deasphalting yields. The variation of solvent composition with deasphalting yield results from the light hydrocarbon solvent characteristic, i.e., as the density of the light hydrocarbon solvent is increased, more deasphalted oil which is progressively more aromatic and higher in molecular weight will be taken into solution, and as the density of the light hydrocarbon solvent is decreased, progressively less aromatic and lower molecular weight deasphalted oil will be taken into solution. Accordingly, it can be appreciated that in order to produce a desirable yield of deasphalted oil, the density of the light hydrocarbon solvent must be controlled. It should be noted that the temperature cannot be varied without significantly altering the physical characteristics, and as the temperature is lowered to increase the density of the light hydrocarbon solvent for increasing the deasphalted oil yield, the viscosity of the petroleum residue phase increases rapidly, thereby lowering the mass transfer coefficient. Thus, the viscosity of the petroleum residue phase virtually becomes so high that it approaches the solid state, and extraction of the deasphalted oil becomes impossible. Accordingly, in order to overcome this difficulty, various solvent compositions have been employed, with the pressure set at the upper limit of the equipment and left constant. The light hydrocarbon solvent composition is usually chosen such that, for the desired yield of deasphalting, the temperature will produce a petroleum residue phase which is low enough in viscosity to allow a reasonable rate of mass transfer.

Although it can be seen that varying the solvent composition is important, this has never proven to be completely satisfactory. Thus, when pure propane is used this generally results in temperatures which are too low and when pure butane is used this generally results in temperatures that are too high, with the high temperature being limited to those levels which are economically available from steam. This has resulted in blends of propane and butane which also have not proven completely satisfactory, since the butane is constantly depleted through contamination in the stripped deasphalted oil and asphalt. Accordingly, the maintenance ofa fixed light hydrocarbon solvent composition presents a continual problem of replenishing the butane losses, and large changes in the light hydrocarbon solvent composition, which are dictated by change in deasphalting yield, are made extremely difficult because of the large solvent inventory generally associated with commercial deasphalting units.

In accordance with the present invention, it has been found that alkane hydrocarbons, such as ethane, propane, butane, pentane, hexane and heptane, as well as alkene hydrocarbons, such as ethene, propene, butene, pentene, hexene and heptene, commonly used as solvents in the deasphalting of petroleum residues, in addition to their well-known characteristic of rejecting high-molecular-weight hydrocarbons on the basis of molecular size, also reject high-molecular-weight aromatics in preference to nonaromatics (paraffinsnaphthenes) of the same molecular weight. Further, it was found that separation was very precise when performed with these light hydrocarbons under the proper operating conditions.

It has been customary in deasphalting operation to utilize a steam coil at the top of the contacting tower for the purpose of generating thermal reflux. Accordingly, by raising the temperature of the material at the top of the contacting tower, the density will decrease and a portion of the hydrocarbon material will be rejected. A separate thermally induced refluxing operation at the top of the column can be entirely eliminated, in accordance with the present invention, by introducing a high-molecular-weight solvent below the feed stock and a lowmolecular-weight solvent above the feed stock. In this manner, it is possible to have refluxing along the entire height of the column itself, thereby eliminating the need for a heating section at the top of the column. The heavy solvent is introduced at the bottom of the column since it is desirable to take more material into solution at this point, and a highmolecular-weight solvent is used to take a greater amount of material into solution. At the top of the column it is desirable to reject material which is accomplished by introducing a light solvent.

SUMMARY OF THE INVENTION In accordance with the apparatus aspect of the present invention, there is provided a contacting tower for separating a petroleum residue containing feed stock into asphalt and deasphalted oil comprising an elongated column formed with an internal chamber. A plurality of annular stator rings are mounted in the internal chamber to form a series of vertically disposed compartments, and a rotor having a series of blades is mounted in the internal chamber such that each of the rotor blades is disposed within each of the compartments. Means are provided for conveying feed stock into one of the compartments. For conveying high-molecular-weight solvent into one of the compartments, means are located below the compartment receiving the feed stock. The high-molecular-weight solvent consists of a hydrocarbon selected from the group consisting of alkane and alkene hydrocarbons containing from three through seven carbon atoms inclusive. For conveying a low-molecular-weight solvent into one of the compartments, means are located above the compartment receiving the feed stock. The low-molecular-weight solvent consists of a hydrocarbon selected from the group consisting of alkane and alkene hydrocarbons containing from two through six carbon atoms inclusive and mixtures thereof, and having at least one less carbon atoms than the high-molecular-weight solvent. in this manner, the high-molecular-weight solvent takes a relatively large portion of the deasphalted oil into solution at the bottom of the internal chamber and the low-molecular-weight solvent because of its lower density, rejects a portion of this deasphalted oil so as to generate reflux at the top portion of the tower.

In accordance with the method aspect of the present invention, there is provided a process for separating a petroleum residue containing feed stock into asphalt and deasphalted oil in a contacting tower. The process comprises the steps of conveying the feed stock into the contacting tower; conveying a high-molecular-weight solvent into one of the compartments which is located below the compartment receiving the feed stock; and conveying a low-molecular-weight solvent into one of the compartments which is located above the compartment receiving the feed stock. The light and heavy solvents have molecular structures in accordance with the description indicated above.

BRIEF DESCRIPTION OF THE DRAWING The above brief description as well as further objects, features, and advantages of the present invention will be more fully appreciated by referring to the following description of a presently preferred, but nonetheless illustrative embodiment in accordance with the present invention, when taken in connection with the accompanying drawing wherein a schematic diagram of a contacting tower is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now specifically to the drawing, there is shown schematically in the FIG. a contacting tower for treating petroleum residue containing feed stock designated by the letter F. The contacting tower 10 is in the shape of an elongated column formed with an internal chamber 12 which is defined by a cylindrical wall 14, a bottom wall 16, and a top wall 18. A plurality of annular stator rings are mounted in internal chamber 12 on cylindrical wall 14 to form a series of vertically disposed compartments 22 within the internal chamber 12. An upper calming grid 24 and lower calming grid 26 are mounted on cylindrical wall 14 and bearing assemblies 28 are secured to the calming grids. Rotatably mounted in the bearing assemblies 28 is a rotor 30 which includes a shaft 32 and a series of rotor blades 34 mounted along the length of the shaft. Each of the rotor blades 34 are located in one of the compartments 22 such that the blades 34 are medially disposed along the length of compartments 22. A variable speed gear motor 36 is coupled to shaft 32 for imparting rotation to the rotor blades 34.

The feed stock F is introduced into one of the compartments 22 by means of a conduit 38; a high-molecular-weight hydrocarbon solvent, designated H is introduced into one of the compartments 22 located below the compartment receiving the feed stock F by means of a solvent conduit 40; and a low-molecular-weight hydrocarbon solvent, designated L is introduced into one of the compartments 22 located above the compartment receiving the feed stock F.

For allowing flexibility in reflux generation, there is provided a low-molecular-weight solvent network 42 which includes three low-molecular-weight solvent conduits 43 44 and 46, each of which has a valve 48 in order to afford adjustment to optimum operating conditions. After optimum operation has been established, two of the valves 48 are closed and the optimum low-molecular-weight solvent conduit is placed in operation.

The high-molecularweight solvent H consists of a hydrocarbon selected from the group consisting of alkane and alkene hydrocarbons containing from three to seven carbon atoms inclusive and mixtures thereof. The low-molecularweight solvent consists of a hydrocarbon selected from the group consisting of alkane and alkene hydrocarbons containing from two through six carbon atoms inclusive and mixtures thereof. The low-molecular-weight solvent L has at least one less carbon atom than the high-molecular-weight solvent H.

A solution of solvent and deasphalted oil designated S is removed from internal chamber l2 by means of a solution conduit 50 connected to top wall 18, and the conduit 50 leads to a recovery system which is not shown in the drawing. A solvent-asphalt mix conduit 52 is connected to bottom wall 16 for conveying asphalt mix designated by the letter M to a recovery system which is not shown in the drawing.

In accordance with the method aspects of the present invention, the petroleum feed stock F is conveyed into one of compartments 22 of internal chamber 12 for effecting a deasphalting separation. The high-molecular-weight solvent H is conveyed to one of the compartments 22 located at the lower portion of internal chamber 12 below the compartment 22 which receives the feedstock F. The low-molecular-weight solvent L is conveyed into one of the compartments 22 at the upper portion of internal chamber 12 above the compartment 22 receiving the feed stock F. The high-molecular-weight solvent H dissolves more material than the low-molecular-weight solvent L at any given temperature. In this manner, both stripping and rectification are achieved in internal chamber 12. The stripping results in the transferring of oil from the feed stock F to the high-molecular-weight solvent H. The rectification results in the exchange of oil between the rising heavy solvent H and the descending reflux. Thus, high-molecular-weight solvent H is utilized in the asphalt stripping section of contacting tower l0, and the low-molecular-weight solvent L is utilized in the deasphalted oil rectification section of contacting tower 10. The utilization of the two solvents in this manner results in flexibility as to overall solvent consumption, as well as improved stripping and rectification.

In accordance with the present invention, the high-molecular-weight solvent H and low-molecular-weight solvent L are introduced into the portion of tower 10 for achieving optimum operating conditions. Thus, the low-molecular-weight solvent is introduced into the top of internal chamber l2 which results in a rejection of material and the heavy solvent H is introduced at the bottom of the internal chamber l2 for taking a relatively greater amount of material into solution.

It should be noted that various components well known in the deasphalting art which are not essential to the instant invention have not been illustrated in the drawing. Accordingly, not shown are the means for recovery of the deasphalted oil, asphalt and solvents, as well as the means for heating, cooling and pumping to achieve the desired operating conditions within the contacting tower 10.

From the foregoing, it can be appreciated that the present solvent deasphalting process and apparatus provides for uniform dispersion in a multistage countercurrent extraction operation whereby the heavy solvent H takes a relatively large portion of material into solution at the bottom portion of internal chamber 12.

In order to more clearly describe and illustrate the advantages of the present invention, reference is made to the following specific examples:

EXAMPLE 1 TABLE I We a W QJYE'AIT 1,000" F. VACUUM RESIDUE 55 Inspection Gravity, AP! Viscosity. SSU at 210 F. Rumsbottom Carbon Residue, wt. IE Nickel, p.p.m. Vanadium. ppm.

' EXAMPLE II TABLE 2.LABORAIORY BATCH BOMB DEASPHALTING Operation 1. Stripping 2. Rectification Kuwait vacuum Solvent-ext. oil phase Feedstock residue from Operation 1 ,Qpuat as nqitls st .00

EXAMPLE 11 Operation 1. Stripping Rectification Kuwait vacuum Solvent-ext. oil phase Rarnsb. carbon residue wt Feedstock residue from Operation 1 Solvent type 65% C /35% C4 80% 03/207 C4 Solvent treat, vol. percent on vac.

residue feed 600 600 Bomb pressure. p.s.i.g 600 600 Bomb temperature, F 164 164 Extracted Extracted Rejected deasphalt- Rejected Solvent free products oil asphalt ing oil oil Yields, vol. percent on vac. residue feed. 35. 96 64.04 21. 40 14. 56 Inspections:

Gravity, API 18.3 1. 1 20. 3 15. 3

Specific gravity, (SO/60 F 0. 9446 1. 0671 0. 9321 0. 9639 Viscosity, SSU at 210 F 4 478 Table 2 shows th'e'bper'iiiing conditions and results of this laboratory operation. The sequence of the operation was as follows:

1. Charge bomb with sample of Kuwait vacuum residue.

2. Charge bomb with high-molecular-weight solvent to give solvent treat as per table 2 operation 1.

. Bring bomb to operating temperature as per table 2 operation 1.

. Agitate contents of bomb until equilibrium is attained.

. Allow phases in bomb to completely separate.

. Withdraw extracted oil phase from bomb and strip out solvent.

. Withdraw asphalt phase from bomb and strip out solvent.

. Recharge bomb with portion of solvent-free extracted oil from step 6.

9. Charge bomb with high-molecular-weight solvent to achieve same solvent to oil ratio as extracted oil phase present in bomb after withdrawal of asphalt phase in step 6.

10. Charge bomb with low-molecular-weight solvent to give solvent treat as per table 2 operation 2.

ll. Repeat steps 3, 4 and 5.

l2. Withdraw deasphalted oil phase from bomb and strip out solvent.

13. Withdraw rejected oil phase from bomb and strip out solvent.

The results of this sequence of operations demonstrates conclusively the stripping action of the high-molecular-weight solvent and the reflux generation by the low-molecular-weight solvent. This action by the two solvents which has now been demonstrated, is the basis for the present invention. It is important to note that reflux (rejected oil) has been generated even though the processing sequence was isothermal. With a single solvent no reflux (rejected oil) could have been generated in this sequence.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

We claim:

I. A process for separating a petroleum residue containing feed stock into asphalt and deasphalted oil in a contacting apparatus comprising the steps of:

conveying said feed stock into said contacting apparatus,

conveying a high-molecular-weight solvent in a liquid phase into said contacting apparatus at a level which is located below the level of said feed stock, said high-molecularweight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from four through seven carbon atoms inclusive and comthan said hi h-molecular-wei ht solvent; and; agitating sai feed stock an solvents in said internal chamber whereby said high-molecular-weight solvent takes a relatively large portion of deasphalted oil into solution at the bottom of said contacting apparatus and said low-molecular solvent takes a relatively small portion of said deasphalted oil into solution at the top of said contacting apparatus.

2. A process of separating a petroleum residue containing feed stock into asphalt and deasphalted oil in a contacting tower formed with an internal chamber including a stripping section and rectification section comprising the steps of:

conveying said feed stock into said internal chamber, conveying a high-molecular-weight solvent in a liquid phase into said stripping section, said high-molecular-weight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from i four through seven carbon atoms inclusive and combinations thereof;

conveying a low-molecular-weight solvent in a liquid phase into said rectification section, said low-molecular-weight' solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from three through six carbon atoms inclusive and combinations thereof and having at least one less carbon atom than said high-molecular-weight solvent; and

agitating said feed stock and solvent in said internal chamber whereby said high-molecular-weight solvent takes a relatively large portion of deasphalted oil into solution at the bottom of said internal chamber and said low-molecular solvent takes a relatively small portion of said deasphalted oil into solution at the top of said interlsham 3. A process of separating a petroleum residue containing 7 8 alkane hydrocarbons and alkene hydrocarbons containcombinations thereof and having at least one less carbon ing from four through seven carbon atoms inclusive and atom than said high-molecular-weight solvent; and combinations thereof; agitating said feed stock and solvent in said internal conveying a low-molecular-weight solvent in a liquid phase chamber whereby said high-molecular-weight solvent into one of said compartments which is located above the 5 takes a relatively large portion of deasphalted oil into compartment receiving said feed stock. said low-molecusolution at the bottom of said internal chamber and said lar-weight solvent selected from the group consisting of low-molecular solvent takes a relatively small portion of alkane hydrocarbons and alkene hydrocarbons containsaid deasphalted oil into solution at the top of said intering from three through six carbon atoms inclusive and nal chamber. 

2. A process of separating a petroleum residue containing feed stock into asphalt and deasphalted oil in a contacting tower formed with an internal chamber including a stripping section and rectification section comprising the steps of: conveying said feed stock into said internal chamber, conveying a high-molecular-weight solvent in a liquid phase into said stripping section, said high-molecular-weight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from four through seven carbon atoms inclusive and combinations thereof; conveying a low-molecular-weight solvent in a liquid phase into said rectification section, said low-molecular-weight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from three through six carbon atoms inclusive and combinations thereof and having at least one less carbon atom than said high-molecular-weight solvent; and agitating said feed stock and solvent in said internal chamber whereby said high-molecular-weight solvent takes a relatively large portion of deasphalted oil into solution at the bottom of said internal chamber and said low-molecular solvent takes a relatively small portion of said deasphalted oil into solution at the top of said internal chamber.
 3. A process of separating a petroleum residue containing feed stock into asphalt and deasphalted oil in a contacting tower formed with an internal chamber, said contacting tower including a series of vertically disposed compartments in said internal chamber and a rotor with a series of blades disposed within each of said compartments, said process comprising the steps of: conveying said feed stock into one of said compartments; conveying a high-molecular-weight solvent in a liquid phase into one of said compartments which is located below the compartment receiving said feed stock, said high-molecular-weight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from four through seven carbon atoms inclusive and combinations thereof; conveying a low-molecular-weight solvent in a liquid phase into one of said compartments which is located above the compartment receiving said feed stock, said low-molecular-weight solvent selected from the group consisting of alkane hydrocarbons and alkene hydrocarbons containing from three through six carbon atoms inclusive and combinations thereof and having at least one less carbon atom than said high-molecular-weight solvent; and agitating said feed stock and solvent in said internal chamber whereby said high-molecular-weight solvent takes a relatively large portion of deasphalted oil into solution at the bottom of said internal chamber and said low-molecular solvent takes a relatively small portion of said deasphalted oil into solution at the top of said internal chamber. 